Top of the address (4)
I believe the answer is:
head
'top' is the definition.
(I know that head is a type of top)
'of the address' is the wordplay.
'of' indicates the answer is hidden within the clue.
'HEAD' can be found hidden inside 'the address'.
(Other definitions for head that I've seen before include "Chief; promontory" , "''and still the wonder grew / That one small ... could carry all he knew'' (Goldsmith)" , "School boss" , "bean" , "Leader; promontory" .)